Age resisting rubber compound and process of making same



Phatented Mar. 21, 1933 UNITED STATES ENT OFFICE" wrm mrn soon, or NITRO, wns'r VIRGINIA, ASSIGNOR ro THE RUBBER snavrcn LABORATORIES 00., on AKRON, OHIO, eoRroRATIon or OHIO class 7 of anti-oxidants AGE 'nnsrsrme RUBBER COMPOUND Ann rnocnss or Maxine I,

No Drawing.

This invention relates to processes for manufacturing vulcanized rubber products and to the products obtained thereby. It is more particularly directed to processes for viilca-nizing rubber wherein there is, incorporated-into a rubber mix of vulcanization characteristics a compound of the type here iii-after disclosedwhereby anti-oxidant or age resisting properties are developed in the vulcanized rubber product. The vinvention will be understood from the following-descriptionand examples ofa preferred mode of operating the process wherein the invention is fully set forth and described. 7

The age resisting characteristics of a vulcanized rubber product can be readily ascer- .tained by subjecting samples of the vulcanized product in a bomb to the action of oxygen under pressure and maintained for several hours at an elevated temperature. The treated samples are then examined and tested, and the results compared with similar results obtained by testing the unaged vulcanized stock. The deterioration in properties suffered as a result of the oxidation -treat mentis indicative of the result that would normally .be expected from that particular stock during service. Such a test is known as the Bierer-Davis aging test and produces an efiect ona vulcanized rubberstock comparable with that resulting from several years of natural aging of the rubber.

Certain compounds, for example aniline,

the acetaldehyde reaction product of aniline hydrochloride, the aldol reaction product of alpha-naphthylamine and the like have been described 'previously'as suitableamaterials to be employed in a rubber mix to lessen the tendency of a vulcanized rubber product to deteriorate by oxidation and toincreas'e the effective life of the product. r 7

According to the present invention, a new or anti-aging compounds has been discovered which upon in corporation into a rubber stock impart such uge r-esistingqualities to the vulcanized stock that samples thereof, when I artificially aged *according to the method hereinbefore ,de

iscribed, retain to a remarkabledegree their .50

original unaged. characteristics. "The com- Application filed September 10, 1929; Serial No. 391,709.

pounds imparting such anti-oxidant characteristics to vulcanized-rubber, as disclosed in the present specification, comprise the sulfur derivative of the reaction product of diamino-diphenyl-methane and beta naphthol.

One of the preferred class of compounds, for example, the sulfur derivative of the reaction product of approximately one molar proportion of ppdiamino-diphenyl-methane and approximately two molar proportions of beta naphthol, was prepared in the following manner: 7

Substantially 11, molar portions of beta naphthol (1584 parts) andsubstantially 5.55

molar portions of p,pd-iamino diphen ylmethane (1100 parts) were placed in a reactor equipped with a condenser for'distillation. The mixture was melted and a quan tity of a catalyst, for example, iodine, equal to substantially 0.4% of the combined weight of the amine and betanaphthol added slowly thereto at a temperature of substantially 200 to 210; over}a' period of abou't'five hours. Additionalheating of the reaction product was carried out in a suitable bath for approximately five to ten hours at a temperature ofsubstantially 200 to 210 C. The re action proceeded smoothlywith the splitting off; of water. The product thus formed was a red'tarry solid, plastic at room'temr'ier'ature.

Substantially one atomic weight portion of sulfur 32 parts) was added to substantially one-fourth of amolar portion of thediaminodiphenyl-methane-betafnaphthol condensation product:(112.5 parts) prepared as described. The mixture was melted, substantially 0.5% of a catalyst or condensing agent, for example iodine, added and the heating continued .for substantially four hours on a suitable bath at approximately 200 to At the end of this period the reaction, whichhad proceeded smoothlywith the evolution ofhydrogen sulfid, was complete. The

solid.

[A sample of this'material was then incorporated in'thewell known manner in a typical tread stock comprising i reaction product so obtained is a pitch-like Parts in the usual manner for different times at Smoked Sheet rubber 100 the temperature given by forty pounds of f black 4O steam pressure per square inch. Samples of Z1110 OXlde the stock thus cured were then artificially A blended mmeml 011 and 2 aged in the manner previously described for slllfur thirty hours at 7 0 C;- and under a pressure pb y -g of 300 pounds of oxygen per'square inch; Antl-oxidant 1.0

The stock was then vulcanized by heating 2 manner for sheets of the stock in'the usual sixty minutes at the temperature given by forty pounds of steam pressure per square inch, that is, 287 thus cured were then artificially aged by heating samples of the said stock in an oxygen bomb for thirty hours at a-temperature V of 7 0 C. and under a pressure of 300 pounds of oxygen per square inch. The results obtained by testing the aged and unaged stocks follow:

Table I r a Modulus of elasticity in lbs/in at elongatmns of Tensile Ultimate Hours aged at break elongaw in lbs/in tion 300 per 500 per 7 7 cent cent 0-- 1465 3375 4100 585 30 1200 1705 390 These results clearly show that the preferred class of materials possess anti-oxidant properties since a sample of a like stock but containing no anti-oxidant when aged under similar conditions melts to a shapeless, sticky mass that is incapable of test. 0 7

Another example of the preferred class of anti-oxidants was prepared by reacting sub stantially one-tenth of a molarportionof the. condensation product of substantially two molar proportions of beta-naphthol and substantially one molarjproportion of diaminodiphenyl-methane (45 parts) and substantially two-tenths of an atomic weight portion of sulfur (6.4 parts) This material was prepared in a manner'analogous to that previously described wherein substantially one atomic weight portion of sulfur was reacted with substantially one-fourth a molar portion of the diamino-diphenylmethane-betanaphthol condensation product withthe exception that the quantity of catalyst was increased to one per cent. The product formed was a brittle pitch-like solid.

Samples of this material were also incorporated in a tread stock comprising:

' Parts Smoked sheet rubber 100 Carbon black 40 Zinc oxide 10 A blended mineral oil and rosin 2 Sulfur 3.25

V Diphenyl-guanidine l Anti-oxidant 1 The stock was'then vulcanized by heating F. Portions of the stock xyg n p qua i the aged and unaged vulcanized 130 The results obtained by testing the aged and unaged vulcanized rubber products are given in Table II; I

'Table II ltlodulus of elasticity in I s H lbs/in? at elcfm- Ttelpsille OUTS galjlOIlSO 8. rear ma 8 Tune of 9 aged inwlbs/ elongav v i a 111 tion 300per 500 per cent cent 30 mamas at 287 "0 1039 2545 3645 040 0 30' 1033 2205 2665 2 s00 60mi11utes at 2s7r 0 1510 3520 4230 555 Do 30 1438 2795 3100 550 90 minutes at 287 1 0 1765 855 4490 505 Do 30 1705 2110 400 g It is seen from Table II that the aged vulcanized rubber stock wherein one of the preferred type of compounds was employed as an anti-oxidant, retained to a great extent its original unaged characteristics.

Another example of the preferred type of anti-oxidants comprises the reaction product.

action product of substantially one-fourth of amolar portion of; the diamino-diphenylmethane-beta-naphthol condensation product and substantially one atomic weight portion o fjsulfur with the exception thatthe quantity of-catalyst or condensation agent was increased to approximately one per cent.

Samples of this material were also incorporated in the usual manner in a tread stock gcomprising P t V r 211 S Smoked sheet rubber 100 Carbon black 40 Zinc oxide"; 10 A blended mineral oil and rosin :2 Sulfur i 8.25 Diphenyl-guanidine r 12 Antioxidant 1 l The stock was then Vulcanized by heating in a'press in the usual manner and the vulcanized rubber product then artificially aged in the manner hereinbefore described at :7 0 Gjand under a pressure of 300pounds of l The results obtained y t ng rubber products are shown in-T ble III.

ilebajsie I The reaction product of substantially one molar portion of the diamino-diphenyl-me' thane-beta-naphthol condensation product and substantially one atomic Weight proportion of sulfur has also been employed in a pure gum stock of the following composition:

Parts Pale crepe rubber 100 Zinc oxide 5 Sulfur 3.5 Diphenyl-gua-nidine 0.8 Anti-oxidant 2.0

Samples of the compounded rubber stock were then vulcanized by heating in a press? in the usual manner and the vulcanized rubber product artificially aged in the manner hereinbefore described at 7 5 C. and under a pressure of 400 the aged and unaged vulcanized rubber stocks follow Table IV Modulus of elasticity in 1bs/1'I'? at elpn- T ile URL Hours E 10115 0 at break mate Tune of cure aged in elongalbs/in tion 300 per 500 per cent cent 30 minutes at 287 F--." 0 241 806 3770 740 0 18 246 394 2725 685 45 minutes at 287 F O 373 1340 4065 680 D0 -i 18 386 1500 2015 555 The data disclosed in Tables III and IV show that the preferred class of materials show exceptional power as anti-oxidants.

The reaction product of substantially one molar proportion of the condensation product of substantially one molar proportion of p,pdiamino-diphenyl-methane and substantially two molar proportions of beta-naphthol and substantially one-half and onefourth atomic weight proportions of sulfur respectively prepared in a manner similar to that hereinbefore described have been incorporated'in tread and pure gum stocks, and have been found, on testing the vulcan ized rubber stock, to possess exceptional antioxidant properties.

In all the examples hereinbefore set forth, diphenyl-guanidine was employed as an ac 'ative of a reaction pounds of oxygen per square 1 inch. The tensile data obtained by testing celerator because to prod uefa vulcanized rubbers ock' thathas particularly poor aging qualities.

"Other accelerators than diphenyl-guanidineycould ofcoarse be employed in conjunction withthe'preferred class of 'mtiwxidints and; in the manner as described Q v The various examples herein-before J set forth in detail are v trativej only and notat soope'ofthe invention. "Other compounding ingredients and other proportions of ingredientsthan those indicated in the various examples may be employed in the "manufac ture of various types'pf vulcanized rubber products, as is well known to those skilled in the art to w ,i'c'hthe invention pertains; The invention is to b'ei under'stood as limited solee 11 'limita tive of 'the t be un e t od as ma l lyfby the claims attached hereto as a part of this specification wherein the invention is claimed as broadly as ispossible in view of the prior art.

What is claimed is:

1. The process of manufacturing sisting vulcanized rubber product which comprises curing a rubber composition of vulcanization characteristics in the presence an age re- I 7 s of an anti-oxidant comprising a sulfur derivtwo molar proportions of beta-naphthol and substantially one molar proportion of p,p-

iamino-diphenyl-methane.

2. The process of manufacturing an age resisting vulcanized rubber product which comprises curing a rubber composition of vulcanization characteristics in the presence of a product formed by reacting substantially one atomic weight proportion of sulfur on product of substantially substantially one molar proportion of a re 1 action product of substantially one molar proportion of p,pdiamino-diphenyl-methane and substantially two molar proportions of beta-naphthol.

3. A vulcanized rubber age resisting characteristics comprising the vulcanization product of a rubber stock containing prior to thevulcanization of said stock an anti-oxidant comprising a sulfur derivative of a reaction product of substantially two molar proportions of beta-naphthol and substantially one molar p,p'diamino-diphenyl-methane.

4. A vulcanized rubber product possessing age resisting characteristics comprising the vulcanization product of a rubber stock containing' prior to the vulcanization of said stock an anti-oxidant comprising the product formed by reacting substantially one atomic weight stantially one molar product tion of p,p'diamino-diphenyl-methane and substantially two molar proportions of beta? naphthol.

. 5. The process of manufacturing an age proportion of sulfur on sub proportion of a reaction, of substantially'one molar properproduct possessing proportion of I use resisting vulcanized rubber product which comprises curing. a rubber composition; of vulcanization characteristics in'the presence of aproduct formed by reacting substantial 1y 3.2 parts of sulfur on substantially parts of the reaction product ofsubstantiazlly 1100 parts of p,pdiamino-diphenyl-methane afiid substantiall 1584 parts of-beta-napht 01. i 6. A 'vulcanized rubber product possessing age resisting characteristics comprising the vulcanization'product of a rubber stock containing prior to the vulcanization of said stock an anti-oxidant comprising a reaction product formed by reacting substantially 3.2 parts of sulfur on substantially 45 parts of the reaction product of substantially 1100 parts of p,pdiamino-diphenyl-methane and substantially 1584 parts of beta-naphthol. In testimony whereof I hereunto aflix signature.

WINFIELD SCOTT. 

